Healthy aging negatively affects performance in specific aspects of cognitive and language function that are crucial for everyday life decisions and actions. Crucial to understanding and promoting successful aging is determining the impact of lifestyle factors such as bilingualism for particular neurocognitive functions. Bilinguals vary in their experience with respect to how, when, and where they use their languages, yet little research to date has examined the impact of diversity of bilingual experiences on language and cognitive function and brain organization. Here, we capitalize upon cutting edge cognitive neuroscience methods to investigate how differences in the social diversity of language use may modulate the impact of bilingualism on language and cognitive functioning over the adult lifespan. In doing so, this research will contribute to our knowledge about how the brain orchestrates its response to the demands of people?s life experiences and the extent to which neurobiological systems involved in language and cognitive control are plastic. This project has three specific aims. The first is to establish a link between the lifespan trajectory of language experience and how this may differentially modulate the impact of bilingualism on cognitive functioning. To examine variability in bilingual language experience, and cognitive control, French-English bilingual speakers ranging from 18-75 years of age will complete a battery of linguistic and cognitive measures. Participants will also be administered a new measure of language entropy, which characterizes diversity of language use across social spheres. Montreal provides a valuable test bed for testing the impact of these experiential factors while holding relatively constant other demographic factors that are known to influence language and cognitive functions (e.g., SES, education). Second, this proposal aims to determine the extent to which lifelong bilingualism provides compensation against age-related declines in language performance. We test to what extent cognitive control is engaged during language processing and how preserved cognitive control abilities in aging affects language performance. Finally, neuroimaging research shows that bilingualism is associated with structural differences in the brain; however, the extent to which bilinguals? contexts of language use modulates these differences remains unclear. Thus, we aim to spell out the neural bases of adaptive changes related to bilingual language experience throughout the adult lifespan. Identifying these changes will not only have implications for further understanding healthy neuroplasticity and how the brain adapts to different kinds of experience, but will also lay the groundwork for understanding atypical brain development and neurological disorders (e.g., learning disabilities, stroke) in our increasingly bilingual population. Altogether, the cognitive and language science community at McGill University provides an environment that is exceptionally suited as a rich training ground in bilingualism and cognitive aging and in using neuroscience methods; this training will provide the applicant with interdisciplinary skills and knowledge as she moves towards an independent research career.